subsurface geology of oil and gas...

Subsurface Geology of oil and Gas Fields

The Faculty of the Earth Resources

Zhu Fangbing

2017.10.

Introduction

Ⅰ. Content

Ⅱ. Characteristics

Ⅲ. Exercises: (Applied Problem)


What? Why? How?

Subsurface geology of oil and gas fields is the key

specialized course for the students majored in petroleum

engineering and exploration of mineral resources

program.

I. Contents

1.Well Data (Foundation)

2.Geology Structure of oil and gas field (Key)

3.Hydrocarbon Reservoir Research (Purpose)

Drilling Geology

Evaluation Oil, Gas and Water Formation

Stratigraphic Classification and Stratigraphic Correlation

Subsurface Structure Research

Formation Pressure and Formation Temperature

Reserves Calculation

Ⅱ. Characteristics

Practice

Inference

Integration


Petroleum Engineering programs are characterized as:

highly unknown, complex in technology, long in running

period, great in investment and more integrative.

Ⅲ.Exercises: (Applied Problems)

1. Well Completion map

2. Oil and water formation identification

3. Well Correlation

4. Geologic Cross Section from Well Data

5. Pressure calculation and analysis

6. Reserve calculation

• Generalized drilling geology

The whole work the geologists do during the drilling.

• Narrowed drilling geology

Geological logging

Chapter 1 Drilling Geology

Before drilling ---- Well Design

During drilling ---- Geological logging and

Formation Testing

Finishing drilling----Well Completion


Section 1 Well Geologic Design

Section 2 Geological Logging

Section 3 Formation Testing

Section 4 Well Completion

Drilling operations are carried out

during all stages of field development.



I. Well Type

II. Well Geologic Design

III. Directional Drilling

Ⅰ. Well type

1. Stratigraphic well

parametric borehole, reference well

(formation, thickness, lithology, etc

provide parameter )

2. Exploration well (Wildcat well )

objective----find hydrocarbon reservoir

3.Appraisal well (Evaluation well)

objective----commercial oil and gas flow

Yanqi basin

4.Development well (Producing well, Water injector,

Gas injector,

Development plan and well pattern

5.Adjustment well

Adjustment development plan

1. Basic data

well number, well type,

well site----well site coordinate, longitude and latitude,

ground elevation, geographic location

target zone, designed well depth

2. Regional geology

Formation

Tectonic setting

Ⅱ. Well Geologic Design

3. Drilling objective

4. Strata profile

predict the location of oil, gas and water bed

Designed well

5.Formation Pressure Prediction

and Drilling Fluid

Before drilling----

During drilling

Drilling fluid property

Well logging

Drilling parameter

Geological logging

Drilling fluid type,

property

Seismic

Adjacent well

Dep

th, m

6.Required data

Geological logging (coring, cutting)

Required sample

Geophysical logging

7. Midway Test

Formation：hydrocarbon reservoir

the formation with oil and gas shows；

Method： wireline test

DST(drilling stem testing)

Purpose：P，Q，K

9. technical and quality requirement

major geological problem

preparatory project

10. geographical and environmental data

meteorological data

terrain feature

8. well structure

11.Accompanying table and figure

①Accompanying table:

② Accompanying figure:

Hierarchical table;

Seismic reflection depth table

Regional tectonic map, geographical location map

Local tectonic well location map;

Geologic profile, seismic time section

Formation columnar section

Ⅲ. Directional Drilling

deviated well----the deflecting well with displacement and

orientation

multiple well----wells group drilled in the offshore platform

relief well----wells design for engineering

purposes

horizontal well----well with maximum

angle approach or

reach 90°.

Advantages of deviated and multiple well

1. It is conductive to find more oil fields, increase reserves and

production;

2. Meet the requirement of underground location;

3. Reduce occupation area, moving and installation time, and before

drilling engineering cost;

4. Control drilling accidents.

A-multiple well； E-stratigraphic reservoir；

B-coast drilling； F-relief well；

C-fault control； G-sidetrack drilling；

D- shady location； H、I、J-salt drilling.

LeRoy, 1977


Section1 Well Design

Ⅰ. Well Type

Ⅱ. Well Design

Ⅲ. Directional Drilling

Chapter1 Drilling Geology

Section 1 Well Design




Section 2

Geological Logging

Objective:

Getting information

Evaluating oil and gas reservoir

Method

cuttings logging

core logging

drilling-time logging

mud logging

Ⅰ. Cuttings logging

Cutting?

Cutting logging: sample interval, delay time,

continues collection and observation cuttings

Feature? Convenience ,

Economy,

Accurate and reliable,

In time,

Information system

Ⅰ. Cuttings logging

1. Well depth calculation;

2. Delay time calculation;

3. Cutting identification and

oil-bearing cutting inspection

Geological logging

Geological logging

1. Well depth calculation

Well depth: the length between bottom-hole to

rotary table

well depth

bottom-hole

ground level

rotary table KB

Drill collar

Bit

Kelly-in

Well depth =drilling tool length + bit +kelly-in

Junction

Drill stem

Kelly

Rotary table

Drilling tool

length

2. Delay time

delay time:

marker, index bed

theoretical calculation

actual measurement

Geological logging

The time which cuttings return

from bottom hole to surface

3.Cutting identification and

oil-bearing cutting inspection

(1)Identification of true/spurious cutting

In the drilling stage, the upper layer usually peel off due to

the long barefoot interval, the changes of mud property and

the frequent activity of drilling tool in the well, then mixed

into the cutting in the hole bottom.

True cutting: fresh section, small pellet, 2-5mm

the pellet shape is related to lithology

Spurious cutting: fuzzy color, big pellet, round-

sub-rounded, obvious abrasion

Geological logging

Cutting description

---far to color, near to lithology

---lamination, name, description

(2)lamination/ layering

A. The occurrence depth of a new component

corresponding to the top interface of the new

lithology;

B. The depth of amount decrease corresponding to the

bottom interface of this lithology;

C. The alternating increase and decrease percentage of

two kind of cuttings indicate lithology interbed.

Geological logging

1. Well depth calculation;

2. Delay time calculation;

3. Cutting identification and oil-bearing

cutting inspection

Comprehensive

cutting logging

1. For stratigraphic correlation;

2. Provide geological evidence for

well log interpretation

3. Provide data for drilling

engineering

Geological logging

Cutting logging comprehensive chart

Cutting logging schematic + well logging curve

Cutting logging comprehensive chart

Scale 1:500

Section2 Geological Logging

Objective:

Getting information


Method

cuttings logging

core logging


mud logging

Put the coring tool into the bottom hole, drill some

core using coring bit. Such a procedure is called coring.

Ⅱ. Core logging

The work that the geologist engaged in, including

core arrangement, observation, description and

mapping is called core logging

Ⅱ. Core logging

1. Coring type and principle

2. Data collection

3. Core description and hydrocarbon-bearing

layer identification

4. Comprehensive core logging chart

5. Sidewall coring

Geological logging

Coring bit

Important first hand information

Hydrocarbon source rock: TOC, A, HC, Ro

Reservoir : ϕ, K, So

1.Coring type and principle

WBM (water-base mud) coring;

OBM (oil-base mud) coring;

SCD: sealing core drilling

Geological logging

Exploration phase---- in order to understand the lithology,

common diameter coring；

Preparation phase---- in order to achieve necessary data, OBM or SCD；

Development phase---- in order to understand the development effect,

large diameter coring

Coring type

Principle—different well type have different coring purpose

and different coring amount

Parametric borehole coring: stratum、 structure 、source-reservoir-cap assemblage

Wildcat well coring： lithology, physical property, oil-gas possibility of oil-bearing layer

Appraisal well coring：lithology, physical property, oil-gas possibility of reservoir

Development well coring： internal reservoir characteristics, development effect

A. Data achievement during coring

Measuring kelly in, calculation drilling depth

Recording Drilling time and cutting

Observing oil and gas show from mud ditch

B. Measure “headspace and bottom space”

“Bottom space”

---the bottom length of core barrel without core

“Headspace”

---the top length of core barrel without core

2.Data Collection

C. Core recovery calculation and

coring logging Coring measuring

Geological logging

Recovery of Core Extraction Calculation

Recovery of core/ core extraction

Coring Numbering ---- mixed number

Recovery core extraction=length of Core/coring footage

5

3 12

Top Bottom

Reliability

Drilling technology

(1)Core description:

lithology, color,

sedimentary structure,

cementing matter,

dips、fracture

3.Core description and

hydrocarbon reservoir observation

Geological logging

(2)Hydrocarbon reservoir observation

A. Gas showing experiment

B. Oil showing experiment

Drop water experiment

Leakage test (sealed, high temperature, 30min)

Fluorescence test

Oil-acid reaction

Acetone experiment

Visual inspection

Drop water experiment

Geological logging

watering layer

oil-bearing formation

saturated oil: oil bearing area> 95%

oil bearing: oil bearing area 70-95%

oil stained: oil bearing area 40-70%

oil spotted: oil bearing area 5-40%

oil trace: oil bearing area <5%

fluorescent show

Visual inspection

Geological logging

4. Core logging comprehensive chart

Cored interval

Lithology

Hydrocarbon-bearing

Electric property

Physical property

Geological logging

Core logging

comprehensive chart

Core logging schematic

Core logging comprehensive chart

Scale 1:50 or 1:100

5.Sidewall coring

The sidewall sampling tool can be used to obtain small plugs

(2cm diameter, 5cm length, often less) directly from the borehole

wall. The tool is run on wireline after the hole has been drilled. Some

20 to 30 individual bullets are fired from each gun at different

depths. The hollow bullet will penetrate the formation and a rock

sample will be trapped inside the steel cylinder. By pulling the tool

upwards, wires connected to the gun pull the bullet and sample from

the borehole wall.

The sidewall sampling tool are useful to obtain

direct indications of hydrocarbons (under UV light)

and to differentiate between oil and gas. The technique

is applied extensively to sample microfossils and pollen

for stratigraphic analysis (age dating, correlation,

depositional environment). Qualitative inspection of

porosity is possible, but very often the sampling process

results in a severe crushing of the sample thus

obscuring the true porosity and permeability.

Section2 Geological Logging

Objective:

Getting information


Method

Cuttings logging

Core logging

Mud logging

Drilling-time logging

1.Basic functions during drilling

2.Mud property

3.Oil and gas show observation

4.Geology factor of influence mud property

Geological logging

The mud circulation system is essentially a closed system. The mud is circulated over and over again throughout the drilling of the well. Of course, from time to time a few additions of water, clay, or other chemicals may have to be added to make up for losses or to adjust the mud’s properties as new and different formations are encountered.

Ⅲ. Mud logging

1. Functions

To bring drilled cuttings from bottom hole to surface;

To control subsurface pressure and to prevent blowout;

To protect sidewall (consolidate the side of the

drilled hole)

To cool bit and lubricate drill string;

To provide subsurface information;

wall building

2.Mud property

Specific gravity

Viscosity

Shear force

Water loss / wall building property

Sand content/sand cut

ph value

Salt content/ salinity

Geological logging

3. Oil and Gas Shows Observation

Oil and gas show

A.oil bloom、bubble: <30%

B.inrush of oil and gas: oil bloom and bubble 30-50%，

C.kicking: oil bloom and bubble >50%

D.well blowout

E.lost circulation, mud loss

Observation mud ditch

A. The time of oil bloom and bubble in the mud ditch;

B. The percentage of oil bloom and bubble in the mud ditch;

C. Hydrocarbon occurrence in the mud ditch

⑴ High pressure zone

⑵ Saltwater influx

⑶ Sand contamination

⑷ Argillichorizon/ horizon/clayey formation

⑸ Lost-circulation zone/leakage formation

4.Geology factors of influence mud property


Objective:

Getting information


Method

cuttings logging

core logging

mud logging


Ⅳ. Drilling-time logging

Pure drilling time required per meter, min/m

Penetration rate reciprocal

Drilling-time logging: It is a logging method that geologist

conducted by using the drill time recorder to record

the needed time for each footage, and draw the drilling

time-depth plot, and then used this plot to study the

formation property and stratigraphic correlation

Geological logging

1. Influence factor

2. Application of drilling-time curve

(1) Rock drillability

(2) Buried depth

(3) Pore fluid pressure

(4) Bit type

(5) Mud property and drilling parameter

1.Influence factor

2.Application

(1) drilling-time curve

vertical coordinata----depth

abscissa----drilling-time

vertical scale 1:500

Geological logging

Measuring interval: 1m

Target zone measuring

interval:0.5-0.25m drilling-time curve

Drilling-time, min

Dep

th(m

)

Change bit

A.Lithology identification, strata profile interpretation

sand shale carbonate

oil-bearing sandstone the fastest

sandstone fast

mudstone, limestone slow

basalt, granite the slowest

B. fracture/cavern identification fracture/cavern --- drilling rate accelerate

Geological logging 2.Application of drilling curve


Objective:

Getting information


Method

cuttings logging

core logging


mud logging


I. Advantages of formation testing

II. Testing Tool

III. Testing Process

IV. Interpretation and Application

Ⅰ. Advantages of formation testing

1. Saving steel and cement, reducing drilling cost;

2. Short time, achieve data quickly;

3. Timely oil reservoir evaluation, and it is the effect method

to find oil reservoir in new exploration area

Conditions：

1. Dense lithology;

2. Smooth sidewall;

3. Formation is not easy to collapse;

4. Good casing programme;

Ⅱ. Testing tool

1. packer

2. by-pass valve, equalizing valve

3. testing valve

4. double shut in pressure valve

5. sampler

6. reversing valve

7. sieve tube, perforated anchor pipe

8. pressure record

6

4

3 2

8

1

7

8

Ⅲ. Testing process

1. trip-in

2. formation testing

3. shut-in pressure measured

4. reverse circulation and trip-out

time

P

B

C1 C2

D

E1 E2

F G A

H B Initial Hydrostatic Pressure

C1 Initial Flow Pressure (IFP1)

C2 Initial Flow Pressure (IFP2)

D Initial Shut in Pressure

E1 Finial Flow Pressure (FFP21)

E2 Finial Flow Pressure (FFP21)

F Finial Shut in Pressure

G Finial Hydrostatic Pressure

（1）pressure card

Ⅳ. Interpretation and Application

Initial flow

Initial shut

Finial flow

Finial shut

Horner

Pressure build-up and pressure drop

curve

Pressure build-up fundamental formula

Horner：

Pws----build-up pressure of bottom hole ，MPa；

Pi ---- Initial pressure，MPa

m---- Slop of straightway in the pressure curve

t---- Production time after open the valve, h △t----Pressure build-up time after close the valve, h

（Ⅰ）Pressure card explain and application

t

ttmPiPws

log

m----slope of straight line section of pressure curve

K---- formation effective permeability, μm2

h --- formation effective thickness ,m；

△t---build-up time after closing test valve ,h

Ф--- formation effective porosity， decimal

μo---formation oil viscosity，mPa.s

Qo---reduced oil production in flow regime，t/d

Bo---formation oil volume factor

ρo---density of stock tank oil ,t/m3

o

ooo

Kh

BQm

31012.2

（ Ⅰ ）Pressure card explain and application

Pressure card application

Calculation of flow coefficient

Calculation of impervious boundary distance

Inferred initial reservoir pressure

Calculation of skin factor

Analysis of formation plugging or damage

Identification of total compressibility

（Ⅱ）Oil, gas and water productivity

1. Oil and water productivity

artesian flowing well ：controlled by choke(flow nipple) and separator,

to calculate oil and water productivity

nonflowing artesian：calculate productivity by height of

level in drill pipe

where： Q----liquid yield ，m3/d（surface）

H----height of level ，m

Vu---volume of drill pipe per unit length，m3/m

t---flowing time，min

？stabilization time：24 hours

Pressure card

Oil, gas and water productivity

Fluid sample under formation condition

1440 Vut

HQ

2. Gas production

orifice flowmeter

Calculate gas production by measure drawdown in

front and back of orifice

packing ring flowmeter

(when gas production in test zone is small, tens or

thousands of cubic meter)

（Ⅲ）Fluid sample under formation condition

Obtain fluid sample under formation condition by sampler taker

sampling before final flow ends

PVT analysis （pressure-volume-temperature)


Well logging

Sidewall coring

Well cementing

Well completion

Well cementing

Well completion

Ⅰ. Well Cementing

Casing and Cement

The borehole needs to be stabilised and the

drilling progress safeguarded. This is done by

lining the well with casing which is cemented in

place.

Ⅰ.Well Cementing

1. Well cementing objectives

2. Casing program

3. Casing and cementing

Ⅰ.Well Cementing


Objectives l To bond the casing to the formation and

thereby support the borehole wall

l To prevent the casing from buckling in

critical sections

l To separate the different zones behind the

casing and thereby prevent fluid movement

between permeable formations

l To seal off trouble horizons such as lost

circulation zones

Ⅰ. Well Cementing

2.Casing program

Casing string

Casing diameter

Casing setting depth

(1) surface casing

(2) intermediate casing

(3) production casing

Casing Scheme---- The borehole needs to

be stabilised and the drilling progress

safeguarded. This is done by lining the well

with steel pipe (casing) which is cemented

in place. In this manner the well is drilled

like a telescope.

Casing Scheme

Casing scheme includes surface casing,

intermediate casing, production casing. Except

for these, sometimes it also includes conductor

and production liner.

Casing joints are available in different

grades, depending on the expected loads to

which the string will be exposed during

running, and the lifetime of the well.

Ⅰ.Well cementing

2. Casing program

(1)surface pipe / surface casing

1

2

3

(2) technical pipe

intermediate casing

(3)reservoir pipe / production casing

well cementing

sidewall casing

It’s the job to set casing and fill cement in annular

space between borehole wall and casing.

Well Cementing

Principle of Casing Cementation

Running casing is the process by which 40 feet sections of steel pipe are screwed

together on the rig floor and lowered into the hole. The bottom two joints will contain a

guide shoe, a protective cap which facilitates the downward entry of the casing string

through the borehole. Inside the guide shoe is an one way valve which will open when

cement / mud is pumped down the casing and is displaced upwards on the outside of

the string. The valve is necessary because at the end of the cementing process the

column of cement slurry filling the annulus will be heavier than the mud inside the

casing and ‘U tubing’ would occur without it. To have a second barrier in the string, a

float collar is inserted in the joint above the guide shoe. The float collar also catches the

bottom plug and top plug between which the cement slurry is placed. The slurry of

cement is pumped down between the two rubber seals(plugs). Their function is to

prevent contamination of the cement with drilling fluid which would cause a bad

cement bond between borehole wall and casing. Once the bottom plug bumps into

the float collar it ruptures and the cement slurry is pushed down through the guide shoe

and upwards outside the casing. Thus the annulus between casing and borehole wall is

filled with cement. The success of a cement job depends partly on the velocities of the

cement slurry in the annulus. The cement has to be placed evenly around each casing

joint. This becomes more difficult with increasing deviation angle since the casing joints

will tend to lie on the lower side of the borehole preventing cement slurry entering

between casing and borehole wall. To avoid this happening steel springs or centralizers

are placed at intervals outside the string to centralize the casing in the borehole.

After the cement is run, a waiting

time is allotted to allow the slurry to

harden. This period of time is referred to

as waiting on cement or simply WOC.

After the cement hardens, tests maybe run to ensure

a good cement job, for cement is very important.

1.Cement supports the casing, so the cement should completely

surround the casing; this is where centralizers on the casing help.

If the casing is centered in the hole, a cement sheath should

completely envelop the casing.

2. Cement seals off formations to prevent fluids from one

formation migrating up or down the hole and polluting the

fluids in another formation.

3. Cement protects the casing from the corrosive effects

that formation fluids may have on it.

After the cement hardens and tests indicate that the job is

good, the rig crew attaches or nipples up the blowout preventer

stack to the top of the casing. The BOP stack is pressure-tested,

and drilling is resumed.

Sometimes primary cementations are not successful,

for instance if the cement volume has been wrongly calculated,

if cement is lost into the formation or

if the cement has been contaminated with drilling fluids.

In this case a remedial or secondary cementation is required.

This may necessitate the perforation of the casing a given

depth and the pumping of cement through the perforations.

Ⅰ.Well Cementing


2. Casing program

3. Casing and cementing

Ⅱ. Well completion

Well completion objectives:

good for borehole stability;

sufficiently expose hydrocarbon reservoir;

good for oil and gas flowing to ground;

good for oil and gas wells normal production ;

good for stimulation measurement,

fracturing, acidifying etc.

simple process, quick well completion, low cost

initial completion

later completion

1. Initial completion

Initial completion----

production casing before broaching reservoirs

barefoot completion/ open hole completion

liner perforation completion

open hole completion

After broaching to the

top of reservoir, trip in

production casing for

completion. Then use

small bits to broach

reservoir. After

completion, reservoir

connect to wellbore

liner completion

After broach the

reservoirs, trip in

liner(slotted casing)

for completion

Apply to single

reservoir with stable

lithology and no

interbedded

reservoirs; wells in

multiple reservoirs

with uniform

character. Widely

used in Fractured

carbonate reservoirs

strong sand

control, prevent

borehole wall

sloughing, large

reservoir, (not

applicable in

interbedded

water), adopts in

loose sandstone

reservoirs.

Initial completion----

production casing before broaching reservoirs

Advantage: good for protecting and liberating oil and gas

reservoirs.

In compacted carbonate reservoirs without the interaction of

interbedded water, it is always adopted.

Disadvantage: interfere in barefoot interval if reservoirs have

different pressure; easy to collapse in weak formation.

2.Later completion

Broaching reservoirs before production casing

perforation completion

liner completion

perforated pipe completion

perforation completion

After broaching oil and

gas reservoirs, trip in

production casing to

the bottom of contributing

zone. Trip in bullet gun

to perforate in oil and

gas reservoirs, penetrate

the casing and cement

mantle to enter formation,

To make channels for oil

and gas flowing into well

liner completion

Broaching to top of

reservoirs, trip in

production casing,

broach reservoir.

Trip in tail pipe, and

connect wellbore

and reservoir by

perforation.


The casing facing

reservoirs is perforated,

and cement basket is

fixed outside the casing

in top of reservoirs.

cement milk in annular

space won’t flow down to

block reservoirs. After

production casing

completion, broaching

cement plug can connect

reservoir and wellbore.

perforation completion After broach reservoirs,

trip in production casing to

bottom of the pay zone.

Trip in specific bullet gun to

perforated reservoirs.

Broach casing and

cement mantle to enter the

formation, to make channels

for oil flowing into wells.

Perforation completion only selectively perforates

in reservoirs. The rest of borehole wall are sealed

by production casing.

Advantage: block up reservoirs, prevent interference

between reservoirs, good for separate well test,

Separate production and separate flood. Remove

influence of borehole wall sloughing to wells.

Strong adaptiveness, widely adopted in completion.

Disadvantage: small reservoir exposure area,

Large resistance when oil flow into wells.

Bad sand control. Bad for production in loose

reservoirs. Reservoirs suffer heavy damage by drill

fluid and cement milk during drilling and completion

liner completion

Broaching to top of

reservoirs, trip in

production casing,

broach reservoir.

Trip in tail pipe, and

connect wellbore

and reservoir by

perforation.

Tail pipe: pipe which trip in wells but

do not connect to well mouth. The upper

part of tail pipe overlap with casing for

100-200m, the annular space outside the

tail pipe is cemented. Perforate reservoirs

to connect well mouth with reservoirs.

Advantage: save steel and cement,

decrease drilling cost


The casing facing

reservoirs is perforated,

and cement basket is

fixed outside the casing

in top of reservoirs.

cement milk in annular

space won’t flow down to

block reservoirs. After

production casing

completion, broaching

cement plug can connect

reservoir and wellbore.

Advantage: sufficient exposure of

hydrocarbon reservoirs, oil and gas

flow fluently, good sand control.

disadvantage: hydrocarbon reservoirs

hard to be blocked after appearing

above water during production.

Cement basket easy to be crushed,

making cement milk intruding into

reservoirs.


well logging

sidewall coring

well cementing

well completion

well cementing

well completion

1. Summary main well type

2. The Objective of appraisal well

3. What is the difference purpose between evaluation well and appraisal?

4. Explain generalized drilling geology

5. Summaries the main contents of drilling geologic design for an exploration

well.

6. Analysis advantages of deviated and multiple well

7. What are the purposes and main methods of geological logging?

8. Analysis the cutting logging features.

9. How to calculate the well depth during cutting logging?

10. Explain delay time. How to get delay time?

11. Coring type and principle

12. Explain mud circulation

13. Explain drilling fluid properties.

14. What are the basic functions of drilling fluid during drilling?

15. Explain the application of drilling –time curve

16. What are the advantages of formation Testing?

17. Explain the pressure card

18. Explain the Casing scheme

19. The purpose of well cementing

20. Well completion objective

Exercise one:

Drawing a summary map for a drilled well

1. Data Provided:

Geological logging (cutting, drilling-time curve, sidewall

coring)

Geophysics logging (R, SP, GR, NGR)

2. Requirements:

To laminate / to stratification

To identify lithology

To identify / recognize oil-bearing formation and water-bearing

formation

To summarize lithological association

Cutting percentage ---- lamination/ layering

A. The occurrence depth of a new component

corresponding to the top interface of the new

lithology;

B. The depth of amount decrease corresponding to the

bottom interface of this lithology;

C. The alternating increase and decrease percentage of

two kind of cuttings indicate lithology interbed.

Geological logging

Spontaneous Potential (SP) Log

Main well logging Methods

Usually the Spontaneous Potential (SP) line on the log shows a more or less straight line opposite impermeable shales, and will show peaks to the left opposite permeable strata. The shapes and amplitudes of the peaks may be different according to the type of formation.

The main uses for the SP curve ---- To detect permeable beds, that is sand vs. shale formations To locate the boundaries between beds To obtain good values for formation water resistivity To correlate equivalent beds from well to well.

Microlog Δt R0.5 R0.45 R4.0 Induction SP

The variations of shapes and amplitudes are related to the lithology.

Spontaneous Potential (SP) Log

Main well logging Methods

The SP deflection is measured with respect to the shale base line. (reference line ----extreme positive side of the SP curve, a straight vertical line) The maximum SP deflections toward the negative side on the log are opposite permeable formations.

The SP curve is important in geological correlation because the

shapes of these curves in different wells for certain geologic horizons

will be comparable.

Electric logs

Acoustic log

Radioactivity log Other well logging

Oil reservoir

aquifer

Oil-water reservoir

Microlog Δt R0.5 R0.45 R4.0 Induction SP

negative

anomaly

subsurface geology of oil and gas...

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